The present invention relates to die cutting machines for making carton blanks, and more particularly to a frame assembly for a lower blanking tool that supports carton scrap during a blanking operation in a die cutting machine.
In the manufacture of cartons, small sheets of paper material having specific profiles are cut out of larger sheets of paper material. These smaller sheets are known as carton blanks which, in turn, are formed into cartons and/or boxes. The blanks are formed during a process known as a blanking operation in a die cutting machine.
In a die cutting machine, the blanks are cut, but not removed from a large sheet of paper material. After the blanks have been cut, the sheet is moved downstream in the die cutting machine to a blanking station where the sheet is positioned over a frame assembly for support. The frame assembly includes an outer frame and an inner grid having large openings which correspond in size, in shape and in position to the profile of the carton blank previously cut. Below the frame is a mechanism for stacking the carton blanks.
At the blanking station, an upper tool is used in combination with the lower tool or frame assembly to knock the carton blanks from the sheet of paper material while holding the scrap material that surrounds the blanks. The upper tool has a support board that moves vertically up and down in the die cutting machine, and the support board typically has a plurality of stand-offs depending therefrom that hold pushers spaced beneath the board which in turn are used to push the carton blanks from the sheet through the lower tool or frame assembly. A plurality of presser assemblies are also mounted in the support board and depend therefrom to hold the scrap material against the lower tool or frame assembly during the blanking operation so that the blanks may be pushed from the sheet. A presser assembly typically includes a presser rail which is biased downwardly away from the support board by a spring so that the rail is positioned slightly below the pushers. As the upper tool is lowered, the presser rail engages the sheet of paper material first such that a scrap portion of the large sheet of material is secured between the presser rail and the frame. The upper tool then continues to be lowered such that the sheet of material engages the inner grid within the frame while at substantially the same time the pushers engage the carton blanks and knock the blanks out of the sheet of material and through the inner grid. The carton blanks then fall into a stacking mechanism below the frame where the blanks are stacked for further processing.
The lower tool used in the blanking operation is typically comprised of a steel outer frame that supports an inner grid. The inner grid is typically comprised of a plurality of lengthwise and crosswise extending bars. In order to secure the inner grid in place on the outer frame, the end of each bar is typically screwed onto attachment pieces which in turn are mounted on the lengthwise and crosswise rails of the outer frame. Since the frame and grid support a sheet of paper material during the blanking operation, the grid must be configured to match or conform to the die cut in the sheet of paper material. In addition, the grid must be reconfigured whenever a different carton blank needs to be produced. Thus, unscrewing the inner grid from the outer frame oftentimes becomes very cumbersome and time consuming. Thus, it is desirable to provide a quicker manner of attaching and removing the inner grid from the outer frame.
Other types of attachment pieces include wedges which are used to clamp the ends of the bars in place. Although these wedges provide a type of quick-connect and quick-disconnect for the bars of the grid, they also have the disadvantage of oftentimes moving the bars slightly during assembly. Movement of the bars, even slight movements thereof, result in the grid being misaligned with the die cut in the sheet of paper material which in turn may result in an imprecise blanking operation.
It is an object of the present invention to provide an improved frame assembly for a lower blanking tool of a carton die cutting machine.
It is another object of the present invention to provide a frame assembly for a lower blanking tool that includes an inner grid that may be easily attached and removed from its supporting outer frame, can be precisely positioned during assembly, and yet maintains its rigidity during normal blanking operations.
It is yet another object of the invention to provide a frame assembly for a lower blanking tool which is easy to assemble, compatible with standard blanking operation machinery, and relatively inexpensive.
In order to accomplish the above objects, the present invention provides a frame assembly for a lower blanking tool of a carton die cutting machine. The frame assembly includes a rigid outer frame, and an inner grid comprised of a plurality of lengthwise and crosswise extending bars for supporting a sheet of die cut paper material during a blanking operation. The frame assembly also includes a plurality of clamps attaching the ends of the bars of the inner grid to the outer frame. Each clamp comprises an upright plate member defining a substantially flat vertically extending inner face, a substantially flat opposite vertically extending outer face, and a horizontally extending upper face. A substantially U-shaped upper cavity is formed in the inner face of the plate member and opens at its upper end to the upper face. The upper cavity defines an upper abutment surface, an opposite downwardly sloped surface disposed at an acute angle with respect to the upper abutment surface, and an upper support surface. An upper wedge member is disposed within the upper cavity for sliding movement along the downwardly sloped surface between clamped and released positions. The upper wedge is also substantially U-shaped and defines a clamping surface disposed parallel to and spaced from the upper abutment surface, an opposite downwardly angled surface disposed to engage against and slide along the downwardly sloped surface of the U-shaped upper cavity, and a base surface disposed substantially parallel to and spaced from the upper support surface of the cavity when the wedge member is in its clamped position. A screw extends through the upper wedge member into the upper support surface and is used to move the upper wedge between its clamped and released positions so as to hold or clamp the end of a bar of the inner grid between the abutment surface of the upper cavity and the clamping surface of the wedge member.
In another aspect, the invention includes the clamping device itself for attaching the bars of an inner grid to the outer frame of the lower blanking tool of a carton die cutting machine. The clamping device includes the upright plate member, U-shaped upper cavity and upper wedge member described above. However, in an alternate embodiment, the clamping device may also include a lower U-shaped cavity and a lower wedge member disposed within the lower cavity for sliding movement along an upwardly sloped surface between clamped and released positions. The lower cavity is preferably a mirror image of the upper cavity, and is used to clamp a bar of the inner grid at two points rather than only a single point if only the upper cavity and upper wedge is utilized. This is particularly useful to attach the lengthwise or machine direction bars of the inner grid as these bars may be taller than the crosswise bars.